Vermiculite, Zonolite, and Stoner Rock

Vermiculite is a naturally occurring mineral used in insulation (brand
name, “Zonolite”), construction, and gardening products.
From 1924 -1990, most of the world’s supply of raw vermiculite
ore came from Libby, Montana. This ore is now known to contain a group
of mineral fibers called “Libby Asbestos.”

Ore from the Libby mine was shipped to many processing plants around
the country. From 1938 to 1989, ore was processed at the Western Mineral
Products plant located at 1720 Madison St. NE in Minneapolis.

At this plant, raw vermiculite was heated until the moisture trapped
in the ore caused it to pop like popcorn. After going through this “exfoliation” process,
the vermiculite was light and porous, making it suitable for insulation.

Some of the ore was left behind after it was heated. This waste material
was known as “crush rock” or “stoner rock.” It
was left in piles outside the plant and was free to anyone. We now know
that this waste rock was contaminated with asbestos.

Waste ("stoner") rock at the former Western Mineral Products site. Circled are grains of pure Libby Asbestos still visible more than a decade after the plant closed.

In NE Minneapolis, people used the waste rock in their yards, gardens,
driveways,
barbeques, and other construction projects. Children from the neighborhood
also played on piles of “crush rock.”

Asbestos and Health

Asbestos
is a mineral fiber that is very toxic if inhaled. It has been known for
many years that workers exposed to asbestos suffer from asbestos-related
diseases. These diseases generally are not diagnosed until 20-30 years
after coming into contact with (exposure to) asbestos.

Asbestos exposure can cause a type of permanent lung damage known as
asbestosis, which causes shortness of breath and increases the risk of
serious lung infections. Asbestos can also cause lung cancer, and a rare
type of cancer known as mesothelioma, which affects the lining around
the lungs and abdomen.

One of the most common effects seen on chest x-rays are changes in the
lining of the lungs, called pleural plaques and pleural thickening. In
some cases, these changes may cause difficulty breathing.

Individual health risk depends on many factors, including how much and
how long a person is exposed, and their age, occupation, smoking and
health history. Residents concerned about health problems associated
with asbestos exposure should consult their physician.

The Northeast Minneapolis Community Vermiculite
Investigation (NMCVI)

Health studies have shown an increase in asbestos-related disease among
people who have worked in vermiculite mines and processing facilities.
There have also been reports of asbestos-related disease among family
member of workers, as well as residents of the surrounding community.

To learn more about exposures to the community and possible health risks,
MDH investigators have interviewed residents living near the site. Former
residents and owners of contaminated properties were also interviewed.
This information, together with additional studies from Libby, Montana,
has helped to identify the extent of asbestos exposure to workers and
the community.

Ways People Were Exposed

Workers had the highest exposure. Sampling data show that some workers
were exposed to asbestos levels that exceed current workplace health
standards.

People who lived with a worker may have been exposed. Workers may
have carried asbestos dust home on their clothing. A household member
who routinely handled or cleaned the dusty clothing would be exposed
to asbestos.

People who had direct contact with the waste were probably exposed
to asbestos fibers. Samples show that the waste contains up to 10%
Libby asbestos. Activities such as playing on the piles, or shoveling
and moving the waste rock cause asbestos fibers to be released into
the air.

People who install, remove or disturb vermiculite insulation in the
home may be exposed. The insulation product has very low or trace levels
of asbestos (less than 1%). However, tests show that activities that
disturb the insulation can produce measurable levels of fibers in the
air.

People living within 1-2 blocks of the plant while the facility was
operating may have been exposed, especially before 1972 when pollution
control equipment was installed. A computer simulation suggests that
fiber levels in the immediate area were higher than normal urban levels.

People living on a property with contamination in the driveway or
yard may have been exposed to trace amounts of asbestos. Asbestos levels
found in driveways and yards were very low. Gardening and landscaping
activities generate very low levels of fiber.

2008/2010 Residual Soil Indoor Asbestos Assessment

Libby asbestos was found and cleaned up on 268 residential properties in Northeast Minneapolis from 2000‐2003. To confirm that the exterior cleanup was sufficient to eliminate exposure to this asbestos, EPA conducted further indoor air and dust sampling in 2008 and soil sampling in 2010. EPA collected and analyzed indoor air and dust samples from residences that previously had Libby asbestos contamination in their yards. Approximately 30 percent (14 out of 48) of residences had detectable, but very low concentrations of Libby asbestos in air, similar to background concentrations. There was no Libby asbestos detected in settled dust samples from any residence. EPA collected soil samples from 40 properties downwind from the Western Minerals Products property to see if there was any residual asbestos contamination from the processing of Libby vermiculite ore. No fibers were detected in any of the soil samples.

Contamination from the Western Mineral plant appears to have been effectively removed from the neighborhood residences and is not expected to harm people’s health. Nevertheless, because asbestos related diseases often have long latency periods (up to 50 years), disease may continue to occur into the future due to past exposure to Libby asbestos from vermiculite processing in Northeast Minneapolis.